This invention refers to a process for transforming the residues left after tanning without chroming and the products thereby obtained, thus allowing waste materials to be recycled. These waste materials include off cuts from skins used in the leather and fur industry, which have previously been sulphured and treated with salt and lime. The process allows products to be obtained from the trimmings of these skins which can be used in agriculture, such as fertilisers, manure and the like, thereby preventing an increase in the volume of rubbish disposed of in rubbish dumps and waste incinerators.
At present, after killing and skinning the animal, and before starting the tanning process, the untreated skins are cured by salting and drying them. The most commonly used curing methods involve the use of salt. The cured skins are soaked in fresh water to remove the salt, blood and dirt and to rehydrate them after the curing process. To remove the hair, the skins are immersed in a solution of lime and water with a small amount of sodium sulphide.
Once this point has been reached, before chrome tanning begins, the skin is cut, leaving certain parts as waste, such as the outline, edges and other parts which are difficult to use in the leather industry. Neither can these trimmings be used to make meal since they have been chemically treated and are thus not suitable for such a use. They are therefore incinerated, or they are thrown away in the rubbish.
These products smell bad in the rubbish dumps and ferment, releasing unpleasant outflows, in addition to increasing the volume of rubbish. Another possible solution to dispose of these industrial by-products is to burn them, but this is an expensive process, which also pollutes.
With the process for transforming the residues left after tanning without chroming and the product thereby obtained, the object of this invention, the aim is to avoid all these drawbacks. In order to do so, the mixture is homogenised and ph modifiers additives, such as an organic acid, semi-metals and noble heavy metals are added. The mixture is put in a pressure vessel and is passed through a filter, the liquid being bottled as an agricultural fertiliser and the solid material being made into peat. In this way 100% of the waste material from trimming the skins may be recycled.
The advantages are twofold. On the one hand, the waste products are not disposed of in rubbish dumps, thus eliminating the corresponding problems such as unpleasant smells, rotting, health risks etc., and not increasing the volume of the areas used for rubbish dumps. At the same time, the costs of incinerating the material are also avoided.
On the other hand, the residual products obtained as a result of the residues being processed using the procedure described in this report, may be used in agriculture, either as products to regenerate the soil, fertilisers etc, or as peat, depending on whether it is the liquid collected after filtering or the solid particles which the filter retains.
Transforming these residual products in active elements is of great interest in terms of their properties as activators in the process of biological fermentation, and therefore they are of great value as activators and soil regenerators used in agriculture and gardening.